text:
Could the center of pressure be not on an aircraft?
I have created the outer mold line of a blended wing body drone and have put it through Ansys Fluent. Using SST k-omega turbulence model and 40 m/s of airspeed. However, the output from the program tells me that the center of pressure of my aircraft is not on my aircraft, but above it and behind it. Is it possible that the center of pressure of an aircraft is not on it?

Likely related -- https://aviation.stackexchange.com/questions/90803/what-means-when-center-of-pressure-is-out-of-physical-dimension-of-wing

@quietflyer the grammer of that question is messy and explaination is hard to understand. So I still can't understand what they are talking about. But does that question states that the center of pressure can be out of the wing? If that is so, then how do we calculate the static margin?

If I understand the details of your question (the first part), the center of pressure should never be completely behind every part of the aircraft structure. That would not be possible.
However to answer the question as you pose it in the last sentence, the CP does not have to be on a part of the design where there is actual aircraft structure. If the aircraft is designed (kinda like a P-38 or a Cessna 337 Skymaster), where there are aerodynamic surfaces which contribute to the overall aerodynamic center, both ahead of and behind an open area where there is no aircraft structure, the CP could be in between pieces of the aircraft. Think Center of Mass, (or Center of Gravity), of a donut-shaped object...
The static margin is the distance between the Center of Mass and the aerodynamic center (or center of pressure - I can never remember which) , Once these two points are located mathematically, the fact that one or both is not coincident with any part of the actual aircraft structure does not affect the accuracy or validity of the calculation of static margin. Think about a seesaw built from 2 seesaws that are bolted together with their seats, at the ends of the two beams that cross over the fulcrum. The center of gravity could be in empty space between the two beams, but the calculations that determine where the balance point is (where to mount the structure on the fulcrum), will still be valid.
Remember, all the mathematical equations, or relationships, we use to calculate aerodynamic forces, and the impact of them on an aircraft are very accurate mathematical models that represent what is actually happening to the aircraft, in a way that allows us to do calculations that result in correspondingly accurate answers to important questions, and can therefore allow accurate predictions about the aerodynamic behavior of the aircraft. They are not what is actually happening! What is actually happening is that molecules within the atmosphere are bouncing off the entire surface of the aircraft, and each collision results in a transfer of momentum (think FORCE), that pushes on the surface at that point, normal, (or perpendicular), to the surface at that point. All the things we think of or use in our aerodynamic equations (like LIFT, DARG, etc.) are aggregate constructs that do not really exist in the real world, they are mathematical fictions constructed to very accurately represent the vector sum of all the individual forces pushing on every single point of the airplane. LIFT, for example, is the component of the sum of all forces that is perpendicular to the flight path of the airplane. Drag, that component that is parallel to the flight path.


text:
How long does a pitot tube last?
Aircraft components need periodic maintenance, this should be the same for the pitot tube that is an essential instrument for pilots. So do you know when should a pitot tube go into maintenance? I can't find relevant information online

The pitot tube its self (the actual metal tube) can be affected by clogging as well as direct impacts or the dreaded pitot tube cover left on before takeoff but broadly speaking are just metal tubes and a somewhat "simple" part for what its worth.
In the US if you are flying IFR your pitot static system needs regular checks, this is generally when issues with the system (and potentially the tube) can be found and lead to replacement.
While some aircraft may have maintenance life schedules for pitot tubes none of the small GA planes I fly require them to be replaced. For planes not flown all that often corrosion can be an issue since they are generally bare metal tubes. The pitot tube should always be checked in your pre-flight walk around.

What about a composite material pitot tube?

@FaitoDayo can you provide an example of one? All the Pitot tubes i have encountered thus far are metal

I am trying to design one, that's the reason behind my question. Also, what materials did they use for pitot tube? Have there ever been a incident when the pitot tube is bent by pressure difference between top and bottom surface of the wing?

@FaitoDayo They are typically metal as they often contain a heating element (which can be problematic for composite structures. As for incidents thats likely the topic for a different question, typically questions do not belong in comments here.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
How does the Urbanaero flying car move forward?
From the pictures of UrbanAero flying car: https://www.urbanaero.com/cityhawk, I can see that can achieve VTOL using the two propeller in front of and in the back of the passenger compartments. However, I am not sure how does it move forward. The propellers don't look like they would rotate, and there are exhaust ports in the back of the vehicle that suggest air would come out and push the car forward. However, this requires an impeller, not a propeller. Could anyone explain this to me? Thank you very much!

I suppose the same way as a helicopter—by pitching down a bit.

Looks like vaporware... not clear that there are any real examples of this concept flying at all, neither forward, backward, or in any direction.

The airplane as such was vapourware from 400 BC to 1903 AD.

@bogl That's true, and as such it received correspondingly little attention on internet message boards during that same timeframe!

@bogl: And a good many things that were vaporware in that time period still are, many of them for good reasons :-)

I guess kind of like this: https://www.youtube.com/watch?v=8oZjl9mSHrY

It would fly forward the same way a quadcopter does:  have the aft motor controller increase current, thereby increasing aft fan lift, creating a pitching moment downward and moving the fan arcs out of planarity with the horizontal, thereby creating a thrust component.  One would have to develop an anti-torque system to counter the increased torque of the rear fan, but that’s not unrealistic.
Now that being said, I agree with Ralph J’s analysis:  That thing is nothing more than idiotic vaporware by some pie in the sky software geek or actual con artists looking to part you from your money.  Flying cars, moisture farming, solar roadways, etc. are apparently very luring for well meaning but scientifically illiterate people who want real life to be like The Jetsons.  Plenty a con man can easily take a pigeon like that for a ride…

Yes, 4 rotors may be better!  A ducted scaled up quad might work.

it is propelled forward by two things in combination: 1) money and 2) gullibility.

@nielsnielsen: Gullibility is bottomless, it's ecstatic.

I can indeed see the two large propeller fans inside the craft, with guiding vanes to direct the exit flow left/right (cannot detect any fwd/aft adjustment). The propellers provide take-off lift, after TO the craft can be tilted forward in order to introduce a forward component of the lift vector, indeed like helicopters do. Temporarily more lift from the aft rotor, point the exhaust vanes slightly sideways to compensate for its increased torque.
Flying with the craft seems to be theoretically possible, but there are serious questions about its safety.

There is no fixed wing, and therefore it cannot glide back to earth upon a power failure. This would have to take place via autorotation, like in a helicopter, but because of the propeller exhaust vane arrangement autorotation airflow would always be vertical through the rotors. Which is not recommended!.
Both the rotors are required to always be operational, otherwise the balance would be distorted, resulting in a crash. Are they mechanically coupled to ensure this?
The power source is electric motors power by hydrogen. This is not mature technology even in electric cars, and are those hydrogen pressure tanks in the picture below? Under high pressure just behind the passengers?

Yeah a flying car might one day be feasible. Even an electrically powered flying car could be done - when all the technology is matured out by experience, since flying takes place at higher altitudes than driving.

In the bottom graphic, interesting choice of tense that they use: "... is the world's first H2 powered vtol."  Their little dream is nothing but a plan right now; to say "will be" would express confidence in the future, although "is hoped to be" would perhaps be more accurate. Upvoted for comments about not-yet-mature technologies.

@RalphJ: I also noted their first "design" was with classic batteries, but it was challenged, so they switched to fuel cells. Currently their "prototype" flies with a classic fuel engine, to test the fuselage and the control panel electronics.

The Urban-Air question, with provided downlink, does seem to show a viable twin rotor design that may provide a more stable flying platform than that experienced with the Avro VZ-9 Avrocar concept from 1959-1961.
Some fairly serious research was done by Avro for use as a modern US Army and Air Force transport vehicle. Although strongly contributing to "flying saucer" legend, excessive gyroscopic effects (before the age of computers) doomed the design.
It is entirely possible 2 rotors may make it much easier to fly.
The Avrocar used vectored thrust for horizontal motion.  For lift, the Urbanaero is essentially a ducted Chinook
helicopter.  At low airspeeds, not a great deal of thrust would be needed to manuever this "air taxi".  The advertisement claims variable pitch rotors.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How to find the battery mass fraction for electrical VTOL aircraft/drone
I am doing an univeristy project to do initial sizing of an electrical vtol drone. Using the aircraft design book from Raymer, I have gotten the battery mass fraction for the cruise, loiter, and climb segment of the mission. However, I can't find a useful value for takeoff and landing battery mass fraction in the book or anywhere else. Is it that climb and takeoff can be count as the same flight segment and the battery mass fraction for landing segment is just a little bit higher than the climb segment?

I'm a bit late here but... have you seriously calculated the battery mass fraction?
The "weight fractions" method is a quick & dirty method to evaluate how much fuel is burned during each flight phase and get the relevant change in weight. For example Raymer suggests a value of 0.97 for the "warmup and takeoff" phases: that value simply means that, due to the burning of fuel, the weight of the aircraft has diminished of some 3% (i.e. the airplane weights now 97% of its MTOW). And so on for all other phases of the mission.
So, what about a battery driven aircraft? Well, the weight of a battery does not change if the battery is full or depleted and therefore the relevant weight fraction is always 1! An electrical aircraft doesn't change weight due to electricity being consumed!
Hopefully your university project didn't contain this mistake at the end...

I read it as the fraction of MTOW that is taken up by the batteries. If you have a range requirement, calculation of the mass fraction can be done.

@PeterKämpf: the op state that they found the mass fraction for "cruise, loiter, and climb segment of the mission" but not the one "for takeoff and landing" so they are clearing doing the wrong thing here... Plus, these latter values are definitely given in Raymer, I've even used one of them in my answer...

It would seem quite reasonable to assume that for a vtol drone (or any other vtol acft) takeoff can be considered to be insignificantly different from climb segment. Only difference would be the short time the drone would operate in ground effect, this phase would last for no more than 5 second.
The same would apply for descent/landing.
I'm not familiar with the concept of battery mass fraction, but the ground effect would work in favour of the drone, making it consume less battery capacity.


text:
On which point are the moment coefficients of the NACA airfoils measured?
On airfoiltools.com website, for example: NACA 2412, they give airfoil data. One of it is the moment coefficient of the airfoil vs the angle of attack of the airfoil. However, these moment data could not be measured against the aerodynamic center of the airfoil. So, where could they measure the moment coefficient?

As information supporting the answer by @PeterKämpf, Abbott and von Doenhoff (1) summarize data from the NACA regarding wind-tunnel tests of NACA 24-series airfoils, and show that for these airfoils of 12 to 18 percent thickness, at a Reynolds Number of 6 million, the moment about the aerodynamic center is at about the quarter chord, slightly more or slightly less, to within about one-percent of the chord length.
(1) Theory of Wing Sections. Dover Publications, Inc. New York. 1959

There is no need for a reference point of a moment. The force vector, however, must be referenced to a specific point which is the quarter point for all decent airfoil data. We have already an answer that explains this in detail here.


text:
Is it possible to work for free in Aerospace Industry for experiences
I am currently in a master's Aerospace Engineering program and are trying to buff up my resume by having some experiences. I heard that in IT industry, there are ways for new programmers to earn experiences by work for free for big IT companies. Is the same method also possible for aerospace industry? Like is it even possible to phone a company and say "Hi, I am a masters Aerospace Eng student and are looking for experiences, could I work as a Engineer-In-Training for free or just as a simple technician so I can get some experiences?"

What country are you looking for work in?  There's legal aspects of unpaid vs paid that vary by country, and some variation in typical job opportunities by country.

@CodyP I live in Canada

Sure you can. What you're looking for is called an internship, and they're hardly limited to just IT work.
Since most internships are targeted specifically at students looking for experience, they're usually coordinated through the school. So, your first step would probably be to contact your professors/advisor/etc. to see what opportunities are available (and to see if they think you can handle working in addition to your course load). If that doesn't pan out, you can look for internships just like you would any other job, via websites and phone calls.

All the interns I’ve worked with got paid.

@Jim There are also paid internships. Most people I've talked to had the unpaid type, but I've never been in any kind of internship myself, so I can only report what I've researched.

Would whoever downvoted care to explain why?

Not my DV for what it’s worth.


text:
How should fuel go through pumps?
I understand that in the fuel system of an aircraft, the fuel first go through wobble pumps--manually driven, and then fuel strainers--for filtering out debris, and finally the engine driven pumps. This is the source: https://angf35eis.com/what-are-aircraft-fuel-system-components/. But I am curious of whether we can change the order of things fuel goes through? Can we go through strainers first? Can the fuel go through engine driven pumps first before going through wobble pump?

Wobble pumps are manually operated boost pumps and are normally upstream of the engine driven pump, often used to help prime it by pre-pressurizing the engine pump inlet before starting. The DeHavilland Beaver had a wobble boost pump as the sole backup pump, which you would use to build fuel pressure before starting, and if the engine pump quit, you could keep flying by stroking the wobble pump (down by your right knee) about once every two or three seconds.
You don't see many wobble pumps today; just about all boost pumps are electric.
The location of the filtering elements like strainer units and the pumps isn't that important from the standpoint of fuel delivery to the engine.  The strainer location is usually determined by where is the lowest point in the fuel system, because that's where you want water to collect to be drained off.
Both engine driven and boost pumps usually are made with a bypass circuit that allows fuel to get past it if the pump isn't working, pulled or pushed by the backup pump, and neither pump cares too much about where it's actually located as long as the suction side is not obstructed.
That being said, the ideal location for any pump is as close to the tank as possible, so that it's doing a maximum amount of pushing and a minimum amount of,... er, sucking.  On most airliners, the boost pumps are right in the tank and pull fuel directly into the pump inlet.  This maximizes resistance to vapour lock, by minimizing the fuel exposed to suction-induced pressure drop, which to the fuel is like going up several thousand feet in altitude.
It's also preferable to locate pumps away from heat sources.  A lot of GA airplanes put their electric boost pumps in the engine compartment along with the engine driven pump, to minimize plumbing and wiring.  Not too big a deal on avgas, but if you operate on Mogas (as I do), which has a lower boiling point and is more prone to vapour lock than avgas, this can become a problem in really hot weather.  My plane has its electric boost pump on the front of the firewall, and I'd like to move it to the cockpit, or ideally, to two separate electric pumps right at the fuel tanks. Moving it from downstream to upstream of the gascolator isn't really an issue.


text:
What kind of signal is outputted from engine fire sensors
Engine fire sensor informs the pilot engine fire and triggers fire extinguisher to release their payload. However, fire extinguisher valves are controlled through pressure operated switches or electrical switch. These valve controls require either pressurized fluids or simple dc currents, not the digital data transmitted from the engine fire sensor to the Engine Information display in the cockpit. Could you tell me what kind of signal is outputted from engine fire sensors?

From a generic system configuration standpoint, the fire sensing loops don't normally trigger the  fire bottles; only the cockpit indicators and alarms. The bottles are fired by separate controls normally on the glareshield or overhead panel.
The pilot needs to be able to fire the bottles at his/her discretion during the engine fire drill.  For example, if a fire alarm goes off right after takeoff, the pilot may delay calling for the drill until the airplane is in a more stabilized phase.
The bottles are fired by electrical squibs (an explosively fired plunger) wired through the firewall shutoff valve switches and normally powered by a very basic battery source bus, so that closing the shutoff valves arms the bottles. You'll normally have guarded pushbutton lights, or handles that you pull and turn to do the arm and fire function.
The fire sensing loops are really just a kind of thermal switch that sets off a fire alarm.  You use a small stainless steel tube with a wire down the center, snaking around the engine, with a voltage applied to the center wire, and a compound insulating the center wire from the outer tube, that becomes conductive above a certain temperature. High temperature applied at any point along the length of the loop closes the circuit.
So to answer your question, whatever monitor unit or central computer is looking for a fire, in most cases the unit will be supplying 28 volts to the loop, and triggering the alarm if 28 volts appears on the return side of the circuit (because there is a hot spot somewhere on the loop that completes the circuit).

why didn't it activate the release mechanism automatically though? wouldn't it be faster and reduce pilot workload? Also, would you mind provide some sources for your description of engine fire sensor set up

Because you may not want it to activate as soon as the alarm goes off.  On a departure, you worry about flying the plane, then deal with the fire when you can divert your attention to the procedure, at least no sooner than autopilot engagement. Also you normally operate the firewall shutoffs and wait, and only fire a bottle if the fire is still going after an interval.


text:
What are the fuel system pressure and temperature requirements of a Williams FJ44 engine?
For my university project, I am designing the fuel supply and control system of an aircraft that use Williams International FJ44-3A engine. However, after scouring through its type certificate datasheets in EASA and FAA, I can't find the fuel pressure and temperature requirement inside. The EASA TCDS said that the fuel requirements are inside the installation instruction. But I can't seems to find them after searching the number of the installation instruction.

actually, the school project is to do preliminary design of fuel supply, cabin pressure, and firefighting system.

The FJ44 uses an internal mechanical pump to provide fuel at high pressure to the engine. At least on the Cessna Citation aircraft that use the engine, the fuel comes from the primary ejector pumps which are submerged in fuel in each engine feed bay (lowest point in the fuel system, holds about eight gals on the Citation Mustang, for example).
The pump utilizes a small jet of high-pressure “motive flow” fuel (from the respective engine fuel pumps). The fuel passes through a venturi, pulls a larger low-pressure flow of fuel from the feed bay, and pumps it back to the engine. Some of the resulting flow also provides motive flow to the scavenge ejector pumps. The primary ejector pump has no moving parts. It operates whenever motive flow is available.
The Citations also have boost pumps that can be used for engine starting, in a low fuel supply pressure condition and for fuel transfer. If the system for the FJ44-equipped aircraft is anything like the Mustang (which uses Pratt and Whitney engines), the boost pumps engage at 4.65 psig and disengage at 6.5 psig. That however is the pressure supplied to the inlet of the primary ejector pump. If the pressure on the motive side of the pump (coming from the engine) remains too low, things will probably get interesting rather quickly for the pilot(s).
So, the answer to your question is that fuel pressure to the engine is not specified, but can be inferred from the boost pump pressure-activated switches. The system simply requires fuel in the tanks and in the engine mechanical pump. As long as those two are there, the venturi effect takes care of the rest. The boost pumps are used when that system is not supplying enough fuel, for whatever reason.
Fuel heating is done by running fuel through an oil heat exchanger. This cools the oil using the fuel, and transfers the heat to the tanks. Temperatures for the Cessna CJ-1, -2, and -3 are shown here. It is interesting to note the document shows the FAA was forced to reconsider its certification requirements for fuel tanks because the maximum temperature of heated fuel being returned to the tanks in Cessna's design exceeds what was before that the maximum temperature required for certification testing of fuel tanks for hot weather operation.
Source: Cessna Citation CJ4 Specification and Description

It is a very useful answer, thank you! Do you know what is the model of the boost pump and the flow ejector pump they use? I may be able to deduce the pressure and temperature requirements using those information.

The ejector pump is just a venturi system. I have no idea what the part numbers are, nor if different aircraft use different part numbers. For the boost pumps you will have to search for parts catalogs and/or maintenance manuals for specific aircraft. Operating manuals will tell you what the minimum pressure is supposed to be before the boost pump engages. In general this type of system requires low pressure but high volume, as the engine injectors require much smaller volume but much higher pressure to feed the engine's combustion requirements.

I added more of the info you need to my answer from another source.


text:
How long should a pitot tube extend from the wing?
It seems that most of the pitot tubes are "L" shaped. However, there are some pitot tubes that shapes like a straight pipe. I am wondering that, for a straight pitot tube installed on the wing, what is the minimum distance the pitot tube need to extend out from the leading edge so it would receive free air and not the boundary layer air?

Wouldn't that depend on the shape of the wing?

Why the downvote? I think its a very good question.

@Christo - The downvote was because the only possible answer to the question is “long enough to get into the free stream” but OP has already indicated that he understands this in the question. The other answer is zero because OP asks for the minimum distance required, and at the appropriate conditions that minimum length is zero.  Other than that this question is akin to “How much horsepower does a car need?”

That’s going to vary from airframe to airframe based on windtunnel data. Ideally you’re searching for a place where the tube orifice has good access to free stream air that is undisturbed by airflow around the airframe, the wing etc. Also placement in a spot where interference is minimized by changes in angle of attack, side slip, etc.  This minimizes discrepancies between calibrated and indicated airspeed.


text:
How much extinguishing agent is needed for an engine fire?
I am quite interested in the firefighting fluid tank choices in turbofan-equipped aircraft. As seen in this picture:

Although this is only the APU, but the fire extinguishing agent bottle looks quite small. would it be enough to extinguish a fire? How much extinguishing gas is used up in one firefighting session for one turbofan (small jet sized turbofan) anyways?

To specifically address the small size of the bottle: these fire extinguishing systems use gas to suppress the chemical reaction of the fire. The amount of the extinguishing agent needed to suppress fire is not particularly high. Halon is one example of a common agent used and only needs to reach a concentration of less than 7% of the volume to be effective. As noted in ymb1's answer, the FAR requires the gas to reach a sufficient percentage of the compartment's volume and must remain above that percentage for some time, considering ventilation.
A fire bottle is typically emptied when used to extinguish a fire, so it's sized based on the volume of the compartment it serves. There may be multiple bottles to allow for additional attempts at extinguishing if needed.


text:
Who make the fuel system, cabin pressurization system, and firefighting system?
Who makes the fuel, cabin pressurization, and engine firefighting system for an aircraft with engines on, or in, the wings? Fuel tanks and fuel pipes, pressurized air pipes and heat exchanger, and firefighting fluid tank and pipes are all located inside the wings. However, the controls of these things are in the fuselage/cabin/cockpit. So is the manufacturer of wings--or its subcontractor--in charge of making those systems, or it is the subcontractor of the aircraft manufacturer in charge of these system and their integration? Are there cost benefits to build systems with most of their components inside a section of aircraft (like tail/wing/fuselage/empennage) be manufactured by the subcontractor of the manufacturer of that section?

They probably don't make them at all, they purchase the components then install them.

Usually in modern aircraft the different system's parts are manufactured by subcontractors. There are industries like Safran (see for example the Safran aerosystem part) or aloft that are taking care of designing these parts and propose them on the market.
In general airplane makers industries are assemblers, they design the frame, they define the specifics of the different systems and later they buy the most possible from subcontractors, taking care of the integrations of the different systems. In general this is true for the most of the components and systems when they are not strictly specific to the design and they do not mean a big change of performance with respect to the concurrency.
I can make an example in the jet engine world. In jet engines the injectors are a strategic component that provoke a big change in performance. For this reason it is a component that is manufactured in-house and kept really secret by the jet engine industry. This is a huge difference with respect to the car engine manufacturers, where the injectors are usually bought from subcontractors.


text:
How aircraft manufacturer decide where to mount the engines on the wing?
How do aircraft designers decide how far from the fuselage should engines be? I am specifically talking about engines that are mounted on, in, or under the wing.

What have you found so far about multiple engines, including when one is shutdown in flight?

This is a veeeeery broad question, if you are happy with veeeeery broad answers, then fine by me.

The tendency is to mount the engines as close to centerline as possible. This mitigates control problems in engine out situations and keeps the wing structure as light as possible: if engines were far from the centerline, the structure of the wing would need to be stronger and thus heavier, and should either/one of the engines fail, the running engine(s) would impose a strong yaw force on the aircraft. On low wing aircraft, engines being below wing and far away from centerline, they would limit the bank angle during landings, maybe making crosswind/gusty landings difficult.
Limiting factors on how close to the centerline the engines can be, are ground clearance, propeller clearance, need to be as vertically as close to the center of mass as possible, and the need for undisturbed airflow. If the engines were right at the root of the wing, on a low wing aircraft the landing gear would need to be very long (assuming the most common setup of wings with upward tilt =dihedral). Also, engines being very close to wing root (top/in/below) would lead to problems with landing gear support structures. If the engines are ones with propellers, you need some clearance from fuselage (more than a few inches) for noise and vibration reasons. Although fighter jets often have intakes right next to the body of the aircraft, this is not optimal, so for jet engines also some distance from fuselage is preferred.
So, it is no wonder the sideways distance of engines in aircraft seems to be pretty standard, with little to no variations between different designs.


text:
Can the cracks found on the A380 wings tear the wing apart?
Given all the press given to the cracks found on some A380 a few years ago, I am concerned about the safety of the current fleet of A380 owned by major airlines, although the planes are fairly new (less than 10 years), and are, I hope, well maintained.
Could their be today a catastrophe resulting from these cracks, especially between the 2-year revision period?

If you're going to worry about cracks in aircraft, outside your control and known and managed by the industry, then you should not fly on any aircraft.  All aircraft have cracks.

Adding to @mins' comment, I think it was the Boeing 787 that was grounded for some time while issues related to its onboard batteries were being worked out. While a different situation, it's not all that different in effect, and there's a real-world example for you...

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Would shooting the tyres prevent a takeoff?
In the movie Fast & Furious 6, among other questionable parts of one scene, they try to prevent a very large aircraft from takeoff.
As opposed to whatever they tried, how effective would it be in preventing takeoff to shoot the tyres?

Would shooting the tyres actually have much effect? Aircraft tyres are somewhat stronger than car tyres and somewhat less strong than, say, mining truck tyres. Shooting car tyres seems to work; shooting mining truck tyres would clearly do nothing.

Prevent a takeoff, no.  Prevent a successful rejection of a takeoff, on the other hand, yes.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Would it be a benefit to install winglets on a Hawker 400XP?
Would it be a benefit to install winglets on a Hawker 400XP? If so how much would the performance be increased?

If the plane is properly designed, probably none or insignificant. Essentially a winglet is equivalent to extending the wing a bit. Now for given speed, altitude and weight, there is some optimal wing span and if the aircraft already has it, extending it does not help. That's why winglets are mostly seen on later generations of transport aircraft—they are usually heavier than the earlier versions, so they should have bigger wings too, but redesigning the wings is a lot of work, so winglets are used as slightly worse, but much cheaper alternative. Hawker 400 XP is not that case.

If that is true, what is the justification for the A320 with sharklets?

@Koyovis there is a restriction on wingspan for things like airport gates.


text:
Airfoils designed for reverse flow
This question might seem strange as almost all aircraft have the air flowing over the wing in only one direction. However if you wanted to design an airfoil would have a good L/D in the forward flow direction, but would also generate lift, or at least not have excessive drag under reverse flow conditions, how would you go a about finding such an airfoil?
The Aerobie flying disc uses an airfoil that looks like a fish. The fish tail creates stability in a spinning disc, but also quite a bit of drag I believe. If stability is not a concern, I think another airfoil shape may provide less drag.
https://en.wikipedia.org/wiki/Aerobie
http://www.aerobie.narod.ru/aerobie.htm

You would copy the cross-setional shape of the frisbee plastic disc toy, which generates lift as it spins and travels through the air by using a shape which looks like the leading edge of a wing no matter which way it is pointing. a wing with two "leading edges" like this is not as efficient as a wing with a tapered trailing edge, but it works well enough to fly significant distances and provide fun for its users.


text:
Does Lift/Drag generally improve at higher Reynolds numbers?
I have been looking at the lift/drag polars for various airfoil profiles.  The L/D ratio seems to improve at higher Reynolds numbers. Obviously different wings are optimized for different speeds, and there are many other factor to consider, but in general terms do wings get more efficient at higher speeds?
I believe a 747 is more efficient than a model airplane because of the higher Reynolds number it operates at. Is this correct?

Yes, the boundary layer that surrounds the airfoil is known to decrease its thickness as the Reynolds number increases; its relative thickness to the characteristic length (the cord for example) scales as $Re^{-1/2}$ in steady flow, and the polar curve becomes more horizontal when Re increases. Meanwhile, lift coefficient increases just a little bit (check this post).
In result, lift-to-drag ratio increases with Re.

An intuitive way to look at it, is that an increase in Reynolds number can be interpreted as a decrease in viscosity taking all other components constant.
$\mathrm{Re} = \frac{\rho u L}{\mu} = \frac{u L}{\nu}$
One can intuitively feel that an object moving through a less vicious fluid will experience less drag. While the lift induced by momentum change in the fluid remains similar (constant $u$ and $\rho$).
It should be noted that at higher Reynolds numbers, the eddy viscosity will increase the perceived viscosity due to turbulence. And at higher Mach numbers you'll experience drag due to compressibility.


text:
If an NORDO airplane approaches and attempts a landing on a controlled airport, is that an automatic emergency?
The airplane never has any communication with ATC etc. but approaches and heads for landing correctly on a controlled airport will that by regulations automatically lead to clearing airspace and airport?

If it's VFR nordo and it enters controlled airspace (C or B), they are not "landing correctly". Are you talking about IFR operations?

Please also specify the region you are asking about.

@RonBeyer It’s legal if it’s the best option in an emergency, which is assumed if you’re 7600. It’s just rare that a B/C airport is the best option since they tend to be ringed by D/E/G airports.

@StephenS, Ron isn't saying it is illegal, he notes, (in quotes) that they are not landing correctly - meaning they haven't established comms per normal FAA procedures.  Yes, it is legal in an emergency, but whether it is an emergency hasn't been answered because the question hasn't been clarified!

@StephenS - In the US, an IFR NORDO aircraft following its flight plan would be “landing correctly” per the FAR/AIM. There are no provisions for a VFR NORDO aircraft to land at a controlled airport without establishing two-way communications. Light-gun signals count. If it is an emergency, the pilot can land wherever he can. Squawking 7500, 7600, or 7500 is recommended, but not required.

Either way, a NORDO aircraft is not an emergency. A VFR aircraft is not required to have a radio.

By itself, NORDO isn't an emergency. As StephanS says in his answer, if you are IFR you continue on your flight plan as filed.
However VFR is the issue... If you are outside Class B or C airspace and you enter Class B or C without clearance, you've violated the airspace. If you have other emergency-level problems and NORDO is just a symptom of that, sure, squawk 7700 and cautiously continue, however I would not ever enter Class B in this circumstance, the potential for major conflicts is just too high.
If you are already in the Class C/B, then you should continue and watch for light-gun signals.
ATC is typically on the ball and will clear airspace around you, but in the post-9/11 world if you violate a Class B area VFR and do not indicate emergency or other issue, expect either a fighter escort or at the very least, a phone number to call when you get on the ground.
Your pilot training included a lot of "lost comms" procedures, you can try listening in on the VOR frequency. If you get low enough, use your cell phone to call the tower. If you only have one radio in the first place, you should be flying with a hand-held backup. Sometimes transmit fails but receive works, so listen to the frequencies and comply with any requests. Try to find a non-towered airport to land at and call the airport you want to go to for prior clearance. There are a dozen things you can do before you violate airspace, do those first, then think about proceeding without clearance.

In an emergency, everything is legal. If your emergency is a radio failure, then squawk 7600 and ATC will recognize the emergency, clear the airspace around you and use light gun signals to clear you to land. But you’re probably better off landing at a non-towered airport where being NORDO isn’t an emergency in the first place.
If you’re squawking 1200/7000 (depending on region), ATC will likely assume you’re just an idiot (or student pilot) who didn’t realize the airport was towered. It happens. They’ll still clear the airspace around you to keep everyone else safe, and they’ll still try light gun signals just in case, but your experience after landing will probably be quite different.

A better context isn't "emergency," but whether the aircraft is given priority.  An emergency may be declared by a pilot, or by a controller, but in either case, the salient intent is to request, and to give priority.  If an aircraft is given priority, it doesn't really matter whether a formal "emergency" declaration is made.  It's about priority.
An aircraft arriving at a controlled airport without any communication will be given priority by necessity.  If the controller cannot communicate with, and thus control the inbound aircraft, he will communicate with everyone else and move them, delay them, turn them, stop them, or clear them as necessary to prevent a collision or unsafe condition.
An aircraft with a communication failure may continue per the flight plan and or clearance and land, and will be given the priority necessary until it can be determined down and clear.  If the failure occurs in visual conditions, the aircraft should divert and land where able without causing an emergency, and notify air traffic control of the failure.
It's important to note that in an emergency, everything is NOT "legal."  One may only deviate from the regulation to the extent necessary to meet the demands of emergency.  One may deviate from any regulation to meet those demands, but should take care not to exceed that necessary, or to abuse the moment.  An emergency, declared or otherwise, is not carte blanche to violate the regulations, or do as one pleases.


text:
What are heat detection sensors and how can they cause a speed error?
From this news article on Saratov Airlines Flight 703:

A report handed down by Russian investigators has blamed human error for the crash of Saratov flight 703, saying the pilots didn’t switch on the heat detection sensors on the plane.

Heat detection sensors sounds wrong as cause of de-icing failure.
Is it a bad translation of the sensor's name? What would be the correct name? Else please explain how the failure to turn on a heat detection sensor cause icing speed error detection.

It seems that the pilots didn't activate pitot tube heaters but the investigation is not completed yet.
"Pitot tube, also known as Pitot probe, is a flow measurement device used to measure fluid flow velocity."
So detection sensors in your question refer to pitot tubes and failure to turn on their heaters in icing conditions can cause incorrect airspeed indication. This in turn may lead to incorrect decisions from pilots or autopilot.

So it is definitely a translation error?  I doubt there would such a thing as a heat detection sensor on the exterior of a plane.

Yes, looks like a poor translation


text:
If the modern airliner was redesigned from scratch, would it look functionally different?
If the modern airliner (Boeing/Airbus) was redesigned from scratch today without any need for "backward compatibility", would it look functionally different from the current design? And if so, what would be different?

What do you mean by backward compatibility?

It's more so a programming term, but meaning the newly designed airliner wouldn't have to be adapted/fitted to any sort of current technology or processes, like airport runway lengths, airport gates, hangar fittings, fuel/electrical connections, etc; starting with a completely fresh slate.

You'll only get opinions here, but from 40 years in the business, my opinion is not much.  Airplanes are a balance of compromises and after much trial and error, dead ends, and false starts, a combination hits a sweet spot in the balancing act and that becomes a near universal configuration.  When someone deviates, it MAY create a new configuration paradigm, but most of the time the reasons the universal configuration works so well are revealed, or rediscovered, by deficiencies in the attempt to strike out on a new path.
And here we are, still building airplanes along the lines of the granddaddy of them all for this particular configuration, the B-47, 73 years later.  Virtually all of the improvements that have followed are related to engines, materials and electronics.
Interestingly, you have a kind of mirror image of the same thing in the bizjet world.  There, the tail mounted twin with fuselage hugging the ground is the design config sweet spot.

Although, it will be interesting to see if the front mounted canard will have much of an impact on biz jets compared to the rear mounted, negative lift horizontal stabilizer.

Been done.  Nearly bankrupted Beechcraft.  https://en.wikipedia.org/wiki/Beechcraft_Starship

I’ve seen one of these many times at KADS. I’m not sure if it’s based there. I will get the tail number next time I see it. It is a shame that the market timing was off. I like the concept of the canard.

The problem was it was overweight, expensive, and the theoretical performance benefit wasn't there so what was the point.  The Piaggio is more successful at this, although it's not a pure canard, but more of a hybrid.  The Piaggio's secret is a carefully profiled forward fuselage that achieves laminar flow for a lot of its length.

I’ll have to see if I’m mistaking the plane at KADS for a Piaggio.

One problem with the Piaggio and the Starship is the main tires right in front of the props.  Better have surgically clean runways, and forget about gravel ops.


text:
What do de-icers do during summer?
I was reading about plane de-icing the other day, and someone posted a comment saying that was their job, and when no planes needed de-icing they just slept/waited in the de-icing truck.
I was looking just now at de-icing jobs, and found one at heathrow that said it was a permanent 40-hour/week job.
So what do they actually do during summer? Do they do a different job or do they just wait in case a random (unlikely) snow storm passes by?

This job listing for a de-icer is a 40-hour per week full time job. Note, however, that it includes "Interior Cleaning" as a substantial part of the job description, including "Removing all rubbish from bins, seat pockets and floors;
Replace old seat pocket literature;
Clean all lap trays, armrests & windows;
Clean toilets & toilet pans; Hoover aircraft" ...and the list continues. I think this answers your question, but since I know little else about the de-icing crew's role I will refrain from publishing my ignorance.

I also see a lot of temp job listings for aircraft de-icers that would be seasonal work.

Just for info, I landed in Kilimanjaro the other day, which is a tropical weather airport and before taking off for the second leg they had to deice the wings. The captain said that the atmospheric temperature was so cold that it cooled down the fuel and when we landed this caused ice to form on the wings. outside temp was 27C on the ground. So I think they still do their job but not as much as in winter.

I don't think it's the case, but some ski instructors switch hemispheres at the right times so they "stay in the winter".

What do air-cooler do during winter?

Most de-icers are run by the airport FBO so the people who work on de-icing in the winter work on other FBO duties such as refueling and the like when there is no de-icing to do. Some de-icers are just hired permanently for winter times.

Do you have any references for your information? I believe that most airlines employ their own de-ice crews. Many FBOs probably offer de-ice services as well. However, I would argue that the majority of de-ice personnel are hired for the purpose of de-icing part 121 aircraft. Also, your last sentence doesn't make sense to me.

It may sound odd, but "permanent seasonal" is a thing - you're on the payroll year-round, but you only work certain months.

@JonathanWalters I think what he meant to say was, some de-icers are just hired permanently for places that are cold all year-round, like Alaska. I'm from a warm place so it took me a minute too.

The permanent seasonal is possible. I find Alaska doubtful since much of the inhabited part of the state is really not cold year round.

@JonathanWalters That's hard to personally believe since I'm from Florida and "cold" and "really not cold" can be taken relatively. I would personally be pretty scared to takeoff in Alaska without deicing even if it was summer.

@DrZ214 Fortunately cold is not a relative term to ice. It either is or isn't.

@JonathanWalters tell that to my fridge when the ice maker broke last summer and kept coughing out some kind of weird sludge

Our state regional airline employs de-icers as technical department personnel. During summer staff is assisting qualified technicians and trucks are used for inspections or repairs (e.g. tail navigation, top anti-collision lights) of aircraft parts located at heights higher than usual ladders can reach, in field works.


text:
How does airspace work with the navy?
Let's say some ships from the US Navy are in the middle of the Pacific Ocean.
Is there anything to stop another country, say the Chinese or the Russians flying around them in circles, either to watch what they're doing or just to piss them off and provoke a reaction?
I mean technically it would be international airspace?

Ah, I think this is called the Flak rule.

anything? yes, the navy fleet itself of course, if the commander wants to, such as when he/she feels such activities is a threat to the safety of his/her fleet.

I mean, in this kind of incident, do you really think either side cares any regulation of any kind?

The reason I ask is because of an article I just read here (a US Navy plane flying over the South China Sea.) The chinese warned them multiple times, but the US just replied saying they weren't in national airspace and can basically do what they want. Would the Chinese have the right to shoot them down? Can the US expect China to do the same thing soon?

I feel this might be better answered on law or politics (with tag "international law").

Related, perhaps even a dupe, although the currently accepted answer is a bit limited, IMO. As others have said, this may also be a political topic.

@cantsay To shoot them down? That's a totally different question. Actually using US and China is not the best example. China and Russia vs Japan is better because this happens very regularly, like 200+ times a year Japan jet fighters are harassing Chinese and Russian military airplanes in international airspaces.

@cantsay that situation is a subtly different case to the general "high seas" situation which you've asked about - China asserts the islands are Chinese, and thus they are in Chinese airspace (per China, the US disagrees). If it was just two ships passing each other far from land, there would be no "national airspace" claim by either side.

@cantsay ...so the disagreement isn't over whether planes have to follow rules in national airspace, or whether they can do what they want in international waters - both sides more or less agree on that. They just disagree on whether the area is national airspace or international waters.

There are a few factors and it may also depend on the relations of the nations.
If the aircraft is unarmed and simply surveilling it may be covered under the open skys treaty. This is largely about overflying other nations territories but presumably applies to over flying marine areas as well.
If the aircraft is armed and potentially making a move to attack the fleet may respond by intercepting. This is more or less the plot of Top Gun.
If the aircraft hails from a friendly nation, they may attempt to contact them and may interrogate their IFF system

There's no international "law" governing this, apart from the general rules like not causing a dangerous situation (so no buzzing the deck at 10ft for example).
That said, common courtesy comes into play, meaning that generally people tend to stay far enough away so as not to impede the operation of the other party.
Of course this might be interpreted differently and sometimes, deliberately or otherwise, aircraft and ships of different countries get too close for comfort for one of them.
Think the incidents where Russian naval air force bombers came close enough to US Navy ships in the Black Sea that their wake staggered people on the fantail of the ships who were filming them.
And yes, on occasion other countries do the same in seas they consider their backyard.

The basic rule for getting close to another aircraft or vessel is never less than 500ft, laterally or vertically.
So when you see film of fighters intercepting eg. Tu95 Bears, or aircraft overflying ships, or ships shadowing other ships (think Russian "trawlers" shadowing RN/USN fleets), they are always 500ft away.


text:
What is a jet engine tolerance for a bird strike?
Similar questions have been asked ; a partial answer is in 14 CFR part 33-76, stating 16 small birds ( 85 g) must be tolerated . But what other qualification tests are there ; for medium and large birds ? I understand the Rolls Royce RB 211 (?) failed the larger bird test and had to be reworked to replace carbon fiber fan blades with titanium. What is the larger bird test ? Accepting that none will survive a flock of geese or ducks.

14 CFR part 33.76 contains a table with bird masses and 3 intake throat areas; the smallest engines must cope with a 1.85 kg bird and the largest with a 3.65 kg bird. Since you list that specification, what is there left to answer? Note that this are the current requirements; those at the time of RB211 development might have been different.

It doesn't much matter, soon there will be no birds.


text:
How are rotorcraft and/or VTOL aircraft handled once they get to an airport?
I am asking this from an ATC perspective ... my experience as a pilot is that they would make helicopters fly the same approach but once they got the airport environment in site where do they go? Taxi over the taxiway at XX feet?  Are they given "hold short" instructions? The whole thing is a big mystery to me.
Do they stay with tower or do they go to ground frequency even though they are still airborne?
And then for VTOL operations I guess those aircraft like the F-35B have wheels so they could land and taxi like a normal aircraft ... is that the procedure?

You usually hear the phrase "air-taxi" or "hover" a lot on Coms with helicopters. They "taxi" by flying close to the ground, but are bound to the same regulations an aircraft has when taxiing. In some cases, I guess when traffic allows, I've seen / heard helicopters taking off and landing directly from where they parked (/will park), which eliminates the need to "taxi"


text:
In-game Air Traffic Control questions
I have been making an AI ATC for a game I have been writing. The channel is mostly dead air but occasionally you can hear some chatter:
http://reskin.us:8081/stream
I am a former airline pilot and a few scenarios come up frequently in the game which I don't have experience with in RL (luckily):
1) Aircraft flying through the class B without talking to approach
2) Aircraft establishing communication with ATC when already inside the class B
3) VTOL operations - to separate aircraft I understand they fly a very normal approach to the airport but then are treated like rotorcraft after that? Do they hand you over to ground control when you are over the numbers or how is that coordinated?
Any controllers out there know what they would say in these cases (if anything) over the radio?
Thanks!

ATC will try to contact the unknown aircraft on the sector frequency and, if that fails, on Guard.  Since they don't have a tail number, they'll call the aircraft by location and altitude (e.g. unknown aircraft 4 miles northwest of XXX at 3500 feet).  At the same time, they'll begin vectoring other traffic away from it to maintain separation; this is similar to how Center/Approach will vector IFR traffic around unknown VFR traffic in Class E airspace, except in Class B they'll also be vectoring VFR traffic (rather than giving mere traffic advisories) as well.  There will likely be missed approaches, TCAS RAs, etc. that have to be dealt with as well.  Still, the only real difference with this happening in Class B vs Class C/D is the staggering volume of traffic affected.
ATC may in some cases ask a friendly pilot in the right place to try to identify the violator.  I've been asked to do that once; we weren't fast enough to get the tail number, but we did identify it as a low-wing single at the reported altitude, which was still useful info for ATC.  I don't know what happened after ATC vectored us back on course; this was years before LiveATC existed.
If/when communication is established, ATC will inform the pilot they're in the Bravo, give them a squawk code and vector them out as quickly and directly as possible without further disruption to traffic flows--without regard for the pilot's desired course.  They'll also ask them to "copy the phone number", as with other violations.  Don't expect any favors from ATC after that, of course, but they're as calm and professional as usual once the immediate safety problem is resolved.
I don't know anything personally about VTOL operations, but I'd assume they'd stay with Tower just like a helicopter--either "cleared to land" on the runway or "land at your own risk" somewhere else on the airport--and wouldn't go to Ground until/unless they needed to taxi within the movement area.


text:
Violation class bravo airspace
I was flying under class bravo airspace at 1800 feet which was the legal altitude 1800 and below but my transponder is off by 200 feet so they thought I was 2000. when I landed and i had to talk to the tower. He did not say anything except be careful and turn your altimeter down next time and be careful. nothing else happened but am I OK? did the get my n number ? i never gave them my name or info.

Sounds like you just got a verbal warning because it was an honest mistake.  Don't worry.  I doubt the FBI is going to raid your house.  The tower folks probably had more important things to do than file violation paperwork for a 200 ft altimeter error.

Disagree that this is a dupe.  He didn't fly into B.  He is asking how to deal with a call from ATC  telling him to be careful.  He's done nothing wrong.  A question about dealing with the fallout from doing something wrong will have a different answer than a question about an ATC mistake.

@acpilot I agree, not a duplicate. I think I voted to close this question as unclear. If Bob can clarify exactly what his question is, it might be worth re-opening. Given our current information, we probably don't know enough to answer his two questions properly ("am I OK?" and "did they get my N number?").

You're probably fine.  File a ASRS form all the same though.
The feds tend to focus on safety of flight issues or gross violations that indicate general incompetence.  Some guy flying below a B shelf doesn't rise to the level of incompetence (because it's not).  Worst case, you caused a resolution advisory for an airliner which, in the grand scheme, is not a huge deal (for you, legally) if you were following the rules (sounds like you were).
If you get a letter, call an aviation attorney.  I doubt it will come to that though.
Keep on flying.

Not clear there was even a violation, but I absolutely agree with the NASA ASRS report filing.


text:
Center Controller with ADS-B question
I don't know anything about planes (mechanics,electroinics,etc...) so bare with me (and the long post)!
In the USA
With ADS-B coming due in a few years, more GA are implementing their planes with ADS-B Out. They will call approach (who knows nothing about it) and in-turn they call us (center) for the answer. Or if they want to be "nice" they just have the pilot dial our frequency and the GA pilot will ask us (not fun sometimes).
All the GA pilot wants to do is verify with "FAA" that their ADS-B is working (center can see that it works, we have a button to toggle on and off). Once we tell them yes/no they are off the frequency. Sounds simple!!
The issue is Center, Tech-Ops, Supervisors.... don't know anything about ADS-B verification. I've taken upon myself to learn this in hopes to inform other controllers.
Questions~~~
What equipment do you have to have for ADS-B?
 Mode A/C transponder only or do you also need Mode S too?
Is ADS-B tied into Mode S or are they completely 2 different components?
Do you need a Mode S transponder to fly? (I think from what I read Part 121 ..commercial you do, but not required for GA if inside the US)
Does the ADS-B get registered to the N number or the air frame (not sure how you split that up)
What is an Example of an ADS-B "code" ? ....to clarify...If it is registered to the tail number, I would assume you have to register a specific "code" to tie the 2 together.
Is the ICAO hex number the same as the ADS-B number/code?
The reason I ask these question is for processing. A GA will call up and we will attempt to put in a flight plan mid flight (they pop up vfr and we try to work this out together) I tell them I need to give them a code to identify them and start a flight plan. I feel like when everything is entered, I am still missing something that needs to be entered to make sure the computer is aware the plane is ADS-B equipped. If it is tied to the tail number, once I create flight plan mid flight, it should auto acquire whether it is ADS-B equipped with no extra info input.
I ask about ICAO hex because I see some ADS-B equipped GA with hex numbers in the system and some do not have hex numbers but still verified ADS-B equipped. I want to know if they are both needed!!!
I also see Commercial flights with no hex number in the system too but I assume they all should.
Thanks, ZOB controller

You have quite a lot of questions about this, but asking a lot at once doesn't work very well with this site's format. It's best if you limit each question post to something that can be answered in a paragraph or two. Making a big topic like this into multiple questions is encouraged.

OK, I was afraid that was going to be the issue.

I think the question can be rewritten to make it fit better here. I'll try to make some changes later today and to answer part of your question.

Thank you very much. Like I mentioned. I don't know anything about planes. I'm just throwing the questions out as I think of them to try to get to the next step in my process. Thanks again

I’m confused about your premise. Why would a pilot call ATC to verify that their ADSB is working?

I am not sure why they would call. I know part of the rebate for GA guys is to do these procedure turns so the system can verify their (pilots) ads-b is working correct. I think they want to verify with us before they go flying around and waste time/gas. I don't think it says in there "rebate rules" they need to verify with ATC to check operations.

I could easily blow them off but I would like to provide a service/help to fulfill their need to complete this.

@JScarry because the FAA requires verification before a rebate can be issued, and because those pilots didn't read the documentation on how to verify it (spoiler alert: you don't need to mention ADS-B to ATC, you only have to operate within certain types of airspace).

FAA has a website now for verifying ADS-B performance  https://adsbperformance.faa.gov/PAPRRequest.aspx  Had to check out my flight here after the transponder was installed to obtain the FAA's ADS-B rebate.

What equipment do you have to have for ADS-B? Mode A/C transponder
  only or do you also need Mode S too? Is ADS-B tied into Mode S or are
  they completely 2 different components?

Either a mode S transponder with Extended Squitter (the ES broadcasts the ADS-s data) which broadcasts on 1090 mhz or a UAT (universal access transceiver) broadcasting only ADS-B data on 978 mhz. Both transmissions are received by FAA ground stations and the aircraft is placed in the ATC computer system where you see the ADS-B info.

Do you need a Mode S transponder to fly? (I think from what I read
  Part 121 ..commercial you do, but not required for GA if inside the
  US)

yes, the advent of ADS-B does not change any requirements for transponders. Someday maybe but not now.

What is an Example of an ADS-B "code" ? ....to clarify...If it is
  registered to the tail number, I would assume you have to register a
  specific "code" to tie the 2 together.

All ADS-B transmissions must output the same transponder code value that the pilot has dialed into the transponder. All ADS-B equipment has some sort of interface the determine Transponder code and that code goes along with the ADS-B transmission.

Is the ICAO hex number the same as the ADS-B number/code?

ADS-B equipment broadcasts transponder code, ICAO hex, and the pilot's choice of flight ID or N number. There is something called anonymous mode and I'm not sure what's sent while in that mode.

I ask about ICAO hex because I see some ADS-B equipped GA with hex
  numbers in the system and some do not have hex numbers but still
  verified ADS-B equipped. I want to know if they are both needed!!!

I've installed approx. 25 ADS-B units in small GA aircraft and every configuration I've seen has a entry for ICAO address. It's possible that you've seen improperly configured units or maybe there's something about it I don't know.

@jScarry> I’m confused about your premise. Why would a pilot call ATC
  to verify

that their ADSB is working?

The A in ADS-B stands for automatic so it works without any control input from the pilot whatsoever. Its just always on without having to actually turn it on. Consequently, he has no real idea whether or not it is working other than the possible absence of a fail message... so he calls ATC to ask him if his ADS-B is showing up or not. Most likely this is his first flight after the install and he just wants to know that he's showing up and that his $7k is actually doing what it's supposed to.

It isn't "always on". I failed my first ADS-B check flight because my transponder was in standby on the ground and wasn't responding to interrogation requests. It didn't start reporting until I turned it before take off. Something I've changed since then, it's on when the avionics are turned on.

@RonBeyer Long ago, the FAA recommended having transponders in standby on the ground. They have now changed that and recommend they be on at all times, and ADSB is required to be on at all times if you're equipped.

Anonymous mode, if enabled, is automatically activated whenever squawking VFR (1200 in the US). It generates a semi-random aircraft ID and uses that instead of the configured one, plus sets a flag to let receivers know it did so. It also suppresses sending the flight and tail numbers. Nothing else changes.


text:
How is airspace in the Persian Gulf determined?
In the wake of the Qatar diplomatic crisis, I saw this image from Business Insider:

How is airspace in the Persian Gulf determined? Why, for instance, does Bahrain have such a disproportionately large amount of airspace for its size? And why is Qatar's airspace predominately to the east of the country? Is this related to air traffic routes in and out of the territory (e.g., lots of Qatari flights fly over Das island, despite it being part of UAE territory)?

Can you link to the article that you found that map? I'm not sure that it is saying the white-ish area is Qatar airspace, for example Bahrain has some small disconnected slice at the Southwestern corner of UAE, which is odd.

Since the source is IVAO that's another reason to doubt the specific accuracy.

ICAO shows that Qatar has no FIR: https://i.sstatic.net/r1dJp.png The white space in the BI picture seems to be the national airspace. The "Bahrain airspace" seems to be Bahrain's FIR minus Qatar national airspace.

This might be the original article the image is from. This other article that shows a similar map. The latter seems to show "Bahrain (OBBB)" encompassing most of Qatar. The latter article says "Qatar has very little airspace; it is largely surrounded by Bahrain airspace (the Bahrain FIR)" which seems to confirm that the map actually shows FIR.

you do realise IVAO is a flight simulator organisation that merely simulates aviation? While they try to be reasonably accurate, there are differences with reality.

Possible duplicate of Can a country ban another country from using its airspace? Can Saudi Arabia ban Qatar from its airspace?


text:
Why is an approach that relies on both LOC and PAPI not considered a precision approach?
I am an aviation layman. I am reading about PAPI lighting system and it seems like it provides vertical guidance, just like the glideslope component of an ILS.
Coupled with a LOC, both vertical and lateral guidance are available to the pilot.
Why isn't such an approach considered a precision approach?
Thank you.

Running on IFR/ILS means you can't really use outside references for guidance, if you could, then you could use the horizon/runway. So what happens when you can't see the PAPI?

I think you're overlooking the primary reason pilots fly instrument approaches: the conditions do not permit flight by visual reference.
The fact that a PAPI provides vertical guidance is more or less useless if you can't see it. Most ILS approaches involve a descent of at least 1500' from glideslope intercept.
If you break out from the clouds at ILS minimums, you can be as low as 200' above the runway surface; at 3°, that's around 3/4 miles from the touchdown zone and the PAPI. It's highly unlikely that the PAPI would be visible prior to that point, meaning the approach would be made with purely lateral guidance.

In addition to the issue of visibility, consider that a PAPI consisting of 4 red/white lights only lets you distinguish between five different states (ranging from all red to all white), whereas an ILS glideslope component will give you a continuous guidance. The latter allows you to spot small deviations or trends much earlier and with significantly higher precision.

A precision approach is one where vertical guidance is provided.  ILS, (former) MLS, and other approaches where there is electronic vertical guidance may qualify as a precision approach (there are some other criteria).  PAPI is not electronic guidance, and therefore would not meet the requirement of vertical electronic guidance on an instrument approach.


text:
DO-254 and microprocessors: how does it apply?
How does DO-254 apply to commercial processors? For instance, I've noticed that "DO-254 certifiable" processors exist. Does that mean that these were designed with inherent redundancy?

I don't see why this would be off-topic, it's about aviation regulations.

Agree with @Federico.  This is a valid question concerning certification of avionics.

I don't know enough to provide a full answer, but it isn't the device that is certified to DO-254, it is the design and verification process used to develop the code.  I suspect that this statement is just a marketing tactic.  (i.e.  if you are designing to DO-254 and are faced with a choice between two devices, you might be inclined to select one over the other simply for the peace of mind this phrase induces...)

DO-254 is for Airborne Electronic Hardware. Redundancy isn't necessarily required for DO-254. I would expect that the processor manufacturer would be able to provide a data package with the necessary documentation if a company were to use it in a DO-254 certifiable product.
In my experience, however, DO-254 is applied for custom micro-coded components only (for the FAA at least). DO-254 was a way to apply concepts similar to DO-178 to things like PLDs, FPGAs, and ASICs to prevent a "firmware" gap in certification.


text:
How Military to Civil Aircraft Transition is made by National Authorities?
As we know military aircrafts are not regulated by civil aviation authority organisations,namely FAA, CAA and etc. Is there any possible way to transform a military aircraft( like helicopters) to civil ones? And if it is, where are these conditions mentioned?

Note for the people answering the question: this question is generic, you should consider also freight or instruction airplanes of army, not just fighters. I read the questions about generic airplanes without official certifications and maintenance record.

Good point, I have added text to my answer to address things like the firefighter ex-military aircraft. The training warbirds fall under the same categories as the other warbirds. There's no special airworthiness category for ex-military training aircraft.

In the US, ex-military aircraft must be issued a special airworthiness certificate before they can be flown as civilian aircraft. Some aircraft may be denied the certificate outright, but most can be flown this way. The hard part is maintaining them, the cost of operating them, and finding qualified people to crew them, including a qualified flight instructor and even a Designated Examiner if the FAA requires a type rating to fly it.
In some very rare cases, it is possible to get a standard or utility airworthiness certificate, but the aircraft must have been previously approved that way before you can do that.
In the majority of cases, the aircraft is given a special airworthiness certificate under the Experimental category, Exhibition subcategory. This means the aircraft can only be operated to exhibit the aircraft’s flight capabilities, performance, or unusual characteristics for air shows, motion pictures, television, and similar productions, and for the maintenance of exhibition flight proficiency. To fly it, you must meet certain experience requirements and in some cases you need to obtain a pilot type rating for that aircraft.
In other cases, if you want to race the aircraft in air races, you can get a special airworthiness certificate for that purpose, to operate the aircraft in air races, practice for air races, and to fly to and from racing events.
To get the airworthiness certificate in the first place you have to submit a maintenance plan for the aircraft to the FAA (often derived from maintenance plans others have drafted) and have it approved by the FAA, and the aircraft must be subject to regular inspections as per the plan.
Source: FAA Experimental Airworthiness Certificates home page
In yet other cases, some military cargo aircraft are converted for missions such as firefighting. Those are exceptional cases, almost unique to the US in that they are not required to comply with many federal aviation regulations.

The Federal Aviation Administration (FAA) has abrogated any
  responsibility to ensure the continued airworthiness of "public-use"
  aircraft, including ex-military aircraft converted to firefighting air
  tankers. Although these aircraft are awarded FAA type certificates,
  the associated certification processes do not require testing and
  inspection to ensure that the aircraft are airworthy to perform their
  intended missions. Source

For other countries I suggest you list the ones you are interested in. I only know the rules for the US/FAA.

Is it possible to get ex-military aircraft approved for non-commercial general aviation purposes? Like if some multi-millionaire with money to burn and a pilot's license decides to buy an old fighter plane to use for commuting between cities that he has businesses in.

@nick012000 There are some very privileged people who do just that with P-51's that were certified as civilian aircraft, and it is somewhat easier to find twin inline engined Cessna O-2's certified the same way from their Cessna Skymaster versions, as well as low and slow birds like the O-1 Birddog, but generally speaking, no, the FAA will not allow that. That said, though, I have to wonder if you could get permission to do that as proficiency maintenance flights... Might be possible but it would be a very hard sell to the FAA.

@nick012000 you may be interested in https://en.wikipedia.org/wiki/Avro_Vulcan_XH558 , which was re-registered as "G-VLCN" for civilian flight and flown at exhibitions for a few years.


text:
Why in helicopter autorotation phase the opposing torque is eliminated?
As you many know, according to Newton's 3rd law for every action there is an equal and opposite reaction, as the main rotor of a helicopter turns in one direction, the fuselage tends to rotate in opposite direction but when there is no engine power during autorotation, there is no torque reaction, why???

"according to Newton's 3rd law for every action there is an equal and opposite reaction" - Newton's third law doesn't say that. Newton's third law says that if one object exerts a force on a second object, then the second object also exerts a force on the first object, equal in magnitude but opposite in direction.

Because the engine is not applying power to the rotors. No engine power means there will be no torque pushing the airframe in the opposite direction.
In auto, the main rotor essentially becomes a pinwheel, kept moving by the air rushing past it...
Auto doesn't really power the rotors, it keeps them moving so that the spinning rotor creates air resistance and slows the descent of the helicopter, and maintains enough inertia in the blades to flare and stop the descent.
Of course, that inertia is only sufficient for one attempt at flaring and stopping descent.

Because the torque to spin it is being generated within the rotor itself, being a forward thrust component of the lift being generated by the spinning blades, like any gliding aircraft.  An autorotating rotor is like two gliders with velcro wingtips going toward each other in opposite directions, who when they pass each other hook wingtips and start to spin around each other, still gliding and moving forward, but forced into a circle who's axis is their inboard wing tips.
What ever rotational force is transmitted to the airframe (a tiny amount) is actually in the same direction as the rotor's rotation; not a torque reaction, just friction drag from the main shaft bearings and sprag clutch.

In autorotation, the engine and gearbox are not applying any turning force, or torque to the rotor system, so therefore there is no torque reaction in the opposite direction.


text:
How to secure an aircraft at a transient parking space?
I've noticed that at many airports, the transient GA parking spaces often don't have tie-down anchors (e.g. bolts drilled into the pavement; heavy steel cables, etc.) or tie-down ropes. They simply have a "T" painted on the ground to indicate the parking alignment. This is true even for many FBO-managed parking spaces.
How should I secure my airplane at these parking spaces? Even if I had my own tie-down ropes, there's nothing to attach the ropes to.
I'm hesitant to just chock the wheels, as this does not prevent a gust of wind from blowing the aircraft around.
Should I ask if there's a patch of grass and use an artificial temporary anchor/Klaw system? Is this even commonly available at your average GA airport?
Note: I only need to park the plane for a few hours, not overnight.

I've been provided with concrete wieghts and tie-down cables at some airfields

Tie downs are generally for overnight or longer.   Nobody ties down an airplane for a visit of a few hours unless there is something forecast in that few hours like high winds or thunderstorms.  And if that's the case, you will want move it somewhere on the airport that has unused permanent tie downs or inside a hangar for the duration of the weather event.
Most screw or spike-in grass anchor systems are useless for serious winds and are easily pulled out.  There are several Youtube videos that demonstrate how ineffective they are, with the exception of one system that uses large spade like blades driven into the ground.

"Nobody ties down an airplane for a visit of a few hours..."? Guess I'm nobody, then :-)

Yep lol...  Seriously, if you have good chocks and it's a normal day, there's really no need unless you're leaving it overnight.  Leaving airplanes on parking brakes?  That's another story.  Chocks are a must.

IDK - lots of small strips have tiedowns, but not chocks laying around.  (Of course I'm more used to the sort of rural/backcountry strips that don't have actual FBOs, and often not anyone else around...)

You should absolutely have chocks on board.  Make some homemade ones if necessary.  If it's a tri gear airplane I usually just chock the nose wheel if it's just for a short time and it's level ground.

If the ramp has tie-downs, I use them, regardless of how long I'll be away. If the FBO needs to move my plane, well, the ramp workers surely have enough experience with the ropes/chains that it's not an issue. If not, do I want them moving my plane?

My experience is that most FBOs have tiedown areas, often on pavement.  Some have them on grass for light airplanes.
It is inconvenient for an FBO to have aircraft tied down, particularly at a busy FBO.  It slows down reconfiguring the ramp, and moving planes up to the lobby for loading.
My understanding, from talking with several FBO managers, is that the FBO is considered to be responsible for the aircraft while it is in their care on their ramp.  If an unexpected front comes barreling in, they have to juggle things and secure the planes.  Assuming that is the case universally (I can't say) then your problem is solved.
Most ramps that I have used have tiedowns.  Some are concrete inlays with cast loops, and some at smaller airfields are concrete inlays with bent rebar sticking out.
I agree with your reluctance to just chock the wheels, and on most planes one does not want to leave the parking brake set (especially in rising temperatures).
My suggestion is that if you are uncomfortable, you call in advance to secure a tiedown, or hangar space. At the very least express your interest in a tie down when you arrive.
Unfortunately, in the US, to my knowledge, there is no specification as to tiedown numbers and availability at airports for transient aircraft.
Of course the problem is not just weather, but includes other aircraft.  I have been in a C-208 while a CH-47 parked adjacently, starts up.  It was an uncomfortable few minutes of getting bounced and buffeted.

"on most planes one does not want to leave the parking brake set (especially in rising temperatures)." <-- Interesting. Could you link to some descriptors of why this is bad practice?

The issue is that most single and light twin aircraft have hydraulic systems which do not have expansion capability.  So as the hydraulic fluid heats while on a warmer ramp, it expands.  The undesirable symptom is that the seals, usually on the caliper blow.  For example on light Cessnas, the hand brake control locks a position.  So the brake system, with the parking brake set, is constant volume, rather than constant pressure.


text:
Are taxiways numbered in a predictable order?
When taxiing at an airport without a full-blown airport diagram (most commonly, a non-towered airport), how does a pilot know whether taxiway A (Alpha) is on one end of a runway, or the other? Or, in the case of taxiway exits, how does one know whether exit A1 is at one end of a runway, or the other?
In other words, are taxiways numbered in a predictable or consistent way? An example would be, “Exit A1 is always located at the easternmost exitway of Alpha”. If they are, is this because of custom or regulation?

Not at all - they'll be built-up in a logical fashion in so much as they're not just randomly assigned but there's no standard beyond the use of letters to denote taxiways and numbers to denote holds. Each airport is free to "make up" it's pattern of taxiways and exits as it sees fit, and many will evolve and grow over time.
For example, at Birmingham International taxiway A (Alpha) takes you from the runway to an intersection with T (Tango) and D (Delta). Bravo is a small spur between the runway and Alpha and there is no Charlie.
At the other end of the runway is Echo and Sierra.
At London Gatwick, Alpha isn't even used on 26/08 - rather it's Juliet, Quebec Hotel and Golf. And neither runway has Echo or Sierra.
In short, there's no substitute for simply knowing (Through the use of chart or local knowledge), looking for signs for asking for a progressive taxi where the controller gives you step by step instructions.

Evolving is a good point. There may have been some logical plan when the airport was first built, but reconstruction over the decades may have rendered it almost unrecognizeable.


text:
Are there any IFR training plugins / addons for Microsoft Flight Simulator or X-Plane?
I am an IFR student, looking for software/plugins/add-ons/extensions to either Microsoft Flight Simulator or X-Plane to enhance the IFR training experience.
Specifically, I was wondering if there was an app that would evaluate my instrument approach in the simulator against the 'nominal' or idealized instrument approach based on the approach plate.
For example, it would evaluate the flight profile to see if I had stayed above the MDA; if I had followed the step-downs appropriately; if I had stayed within the required procedure turn completion distance, etc.
Is there any such software like this, or is specifically tailored towards IFR training?

Both sims allow you to do a review of your flight where you can see both plan views and vertical profiles of the flight to analyze the results.  This can be especially useful when analyzing the results of attitude instrument flying like A and B patterns, etc.
CloudAhoy does allow integration of flights from X-Plane for review as well.
ATC is a bit better in games like FSX and Prepar3d, but I’d guess there are live ATC available in realistic multiplayer sessions of X-Plane as well.
One real pain in the butt about those Sims is just how out of date they are in terms of navigation databases, etc.  you really can effectively simulate approaches if you can load and practice the latest ones.
That being said the games are excellent to practice basic attitude instrument flying in as computers can simulate that very well sans the vestibular distractions which accompany flying in IMC.  You can also practice partial panel and other IFR emergencies here as well.

I agree, also navaids can be updated. FSX/Prepar3d for example https://www.aero.sors.fr/navaids3.html is good, for x-plane purchase them from Navigraph or Aerosoft. (https://forums.x-plane.org/index.php?/forums/topic/134304-navaid-updates/)


text:
How short does a trip need to be before flying is less safe than other forms of transportation?
It's often mentioned that flying is the safest form of transportation, and no doubt this is true when considering only a long-haul trip. There's no doubt, for example, that driving (or taking a train or bus) 3,000km would be more dangerous than flying the same distance.
However, most flight crashes occur at take-off or landing and so I suspect there must be a break-even point after which flying becomes more dangerous than alternatives. For instance, if a flight is only 300km, would it be safer to drive?
For the purposes of this question, it can be assumed that I'm talking about OECD countries, which by and large have very high standards for both flight safety and the safety of other forms of transportation.

I suspect you'd have to hypothesize an airline flight on the order of a few miles before you could get the numbers to work out the way you're suggesting, and at that point economic reality would intrude, because such fights would be expensive beyond all reason. And no quicker than driving, given time taken to board & deplane & etc. Commercial aviation (in the developed world) is literally safer than living (in deaths per million man-hours), so even with the higher risks at takeoff & landing, it'll be hard to get the lines to cross.

Would regularly scheduled helicopter routes count? There are and historically have been airlines operating dedicated short (10-20min), regularly scheduled, and standard fare helicopter routes. Example JFK->NYC and SFO->OAK (Historical)

The 737 MAX has some pretty short flights.

I believe airlines (how many?) do a lot of short flights in Hawaii for the Island hopping. Lots of quick pressurizations and depressurizations cycles. The only incident that comes to mind is Aloha Airlines Flight 243.

I'm assuming if your flight lasts less than 100 metres in a jetliner, it would be very unsafe indeed.

This question seems to imply that touch and go's add danger to flying...

Safer than what? Buses and cars, no chance. But since Amtrak's inception, it's been a footrace, with the stats rocking back and forth depending on the last big accident... The DC-10 troubles, Gunpow, 9/11+Queens, Big Bayou Canot. Between that last and a phenomenal run of luck for the airlines, they hold the trophy.   But Amtrak finally has PTC which will prevent a range of accidents, and air is unable to achieve that innovation.

Note: This does not take travel to/from the airport into account.
The Wikipedia page on aviation safety has a nice table with deaths per journey, time and distance (based on data from the UK between 1990 and 2000):

Car: 40 deaths per billion journeys, 3.1 deaths per billion km
Aircraft: 117 deaths per billion journeys, 0.05 deaths per billion km

Assuming that car accidents are equally distributed along a journey, we only need to consider the 3.1 deaths per billion km. Further assuming that all aircraft accidents are related to takeoff and landing (i.e. once per journey), we only consider the 117 deaths per billion journeys. While the first assumption is probably reasonable (there are differences between types of road though), the second one is not quite true since aircraft can also develop problems during cruise.
With these basic assumptions, we can calculate when the expected number of deaths are equal:
$$ N_\text{death} = 117 \cdot 10^{-9} = 3.1 \times \frac{d}{10^9 \, \text{km}} \; \Leftrightarrow \; d = \frac{117}{3.1} \, \text{km} \approx 38 \, \text{km} $$
So any flight longer than 38km is safer than driving the same distance.
Let us now try to take the cruise part for aircraft into account. According to this page 20% of all fatalities are due to accidents during cruise. We can subtract 20% from the 117 deaths per billion journeys (so this only takes the parts of the flight into account that happen once per journey). Modifying the 0.05 deaths per billion km is not so straight forward. Since most of the distance is traveled in cruise, I am going to be conservative and just leave this number unchanged, therefore providing an upper limit on the deaths per km.
Now, we can make a more accurate comparison:
$$ N_\text{death} = 0.8 \times 117 \cdot 10^{-9} + 0.05 \times \frac{d}{10^9 \, \text{km}} = 3.1 \times \frac{d}{10^9 \, \text{km}} $$
$$ \Leftrightarrow \; d = \frac{0.8 \times 117}{3.1 - 0.05} \, \text{km} \approx 31 \, \text{km} $$
This is actually lower now, because the deaths during cruise are irrelevant for such a short flight. And this gives the final answer: Flights longer than 31km are safer by airplane than driving the same distance by car.

Nice answer based on statistic extrapolation. Of course, there is no evidence that the extrapolation is valid for such short flights. I would expect that landing 4 minutes after start is stressful and results in a higher accident rate.

@bogl Good point. While there are shorter flights, I could not find a statistics for how safe these are. But I agree with you, the accident rate is probably higher, although not by orders of magnitude, so the answer should not change too much.

The fault in analises like this is always the same: it assumes an "average" driver. But the fact is that most car accidents, especially serious ones, are caused by gross negligence. Of course, this isn't a problem that this answer can solve but just once, I'd like to see driving statistics that exclude drunk drivers, morons who text and drive etc. and see what are the odds of an accident if I'm a person who keeps proper focus on driving.

@Davor yes. Then again, even though most accidents are caused by negligence, even a careful driver still has a considerable risk of getting involved in such an accident. — Anyways, a more interesting comparison would be plane vs train, not car.

I would guess the danger of driving per km actually increases with the length of the trip, because tired drivers make more mistakes. However, I have no idea how big this effect could be. Maybe someone collects on how long the drivers involved in an accident had been driving.

@JiK I don't have the details handy, but have seen statistics more than once that most car accidents occur near the driver's home.  Of course, this could be the end of the journey and not the start.

@AleksG there is also a difference between accidents and fatal accidents. I was involved in a few accidents, almost all near my home. But I am still alive and so was everyone else involved after the accidents. The most serious accident cost a few thousand euros to fix the cars. I am not so sure that most fatal car accidents occur near the drivers homes.

@AleksG that's because most car journeys occur near (definition?) the driver's home

Short flights may well be more dangerous than long flights per km, especially if the aircraft you are on does frequent short flights. Equipment failures due to low-cycle fatigue depend on the number of takeoffs/landings, e.g. Aloha Airlines Flight 243, on an aircraft that did frequent short hops in a corrosive environment.

"Note: This does not take travel to/from the airport into account." which is kinda the problem with this type of analysis. The most dangerous rounds are country roads and if you have to drive down those then you will probablly have to drive down them whether the bulk of your journey is going to be made by plane, train or motorway.

@JiK the type of carriage way makes more difference than just tired due to long haul , people are tired (e.g. hungover or sleepy) during normal driving e.g morning commutes, but much of the same features of airline traffic, seperation (median) , spacing (lanes), and controlled entry/exit (onramps/offramps) make highway travel safer despite the faster speeds and longer distances. Many fatal accidents occur due to head on collisions on undivided highways world wide .

This also does not take into account the type of aircraft. Large commercial airliners are operated with much higher standards of safety than small GA aircraft. A short flight is likely to be aboard a small aircraft, and therefore much more dangerous than a long flight.

Doing a measurement based on just "deaths per km" is also kind of iffy, since you can say that the crew of the ISS has them all beat, circling the globe every 90 minutes, thus travels ~682,400 km per day, and so far zero deaths on board.  (There's been a few going to or from the station, but if we don't count driving to the airport, then we can't really count those either.)

@DarrelHoffman Whereas "Earth" is very UNsafe--4.5 deaths per 1000km (traveled with respect to the CBR).

@user3067860 Indeed, the Earth has a nearly 100% fatality rate if you consider how long it's been travelling...

@bogl On the other hand, accidents on landing are often caused by unexpected conditions at the destination airport. For such a short flight, conditions are unlikely to have changed much since takeoff.

It's a theoretical answer. No more, and no less.

@DarrelHoffman Less so than you might thing... for example, if we froze everything at this point in time there would be a ~7% survival rate of humans. https://www.prb.org/howmanypeoplehaveeverlivedonearth/

Note that the UK has a relatively low number of driving fatalities (even for OECD countries). The US has at least twice as many, 7.3 per billion km, adjusting for that we get around 80km and we are close to driving actually being saver for some short but realistic flights. It is definitely within the margin of error for some flights to be more dangerous than driving and so the "fact" that flying is much safer than other forms of transport is probably quite an overstatement. And that is already when we are comparing to the most dangerous form of transport, i.e. driving,...

... when comparing against travelling by train I think it will be more dangerous at much larger (if not all) distances.

To put the breakeven distance in perspective, the distances from IAH to HOU, from IAD to DCA, from JFK to EWR, and from LHR to LGW are all further than it is.


text:
Are matches in checked baggage a safety problem?
A friend of mine checked in on Singapore Airlines a bag which had a box of matches in it. They are regular matches and not the "strike against anything" type.
My friend subsequently realised that these were banned on that airline, and went back to the baggage check-in location. The baggage check-in staff said that it was not worth the bother to retrieve them, and that security personnel later on would remove the matches if they thought they were a problem.
Presumably there is some chance the personnel later on would miss the matches, but the staff did not seem to bothered by this, which suggested to me that maybe there was no genuine safety problem here.
What's the rationale for this rule existing? Of course in life on the ground matches do not generally spontaneously ignite, but I wondered if maybe different conditions in the cargo hold made matches more likely to ignite on their own?

Not an answer, but according to Annex 18 of Chicago Convention, matches are "dangerous goods" of class 4.1, flammable solids, substances. They are not prohibited on aircraft, but are subject to rules, I believe explanations are found in this document and its technical specifications Doc 9284 (large 1,000 pages document).

To answer to your question, yes.  But the question in your post does not match the title.  Which question are you asking?

The reason that matches are banned on most airlines is not that they might accidentally catch fire. Especially not in the cargohold of the plane. Sometimes the cargohold is not even pressurized. and a lot of safety measures are taken to prevent cargo fires, including suppression systems in case this does happen.
Most likely the ban is for carry-on baggage. Most airlines will allow you to take a lighter with you, but only 1.
The reason is that if someone wants to start a fire in the passenger cabin, this is not as easy with a lighter.
A box of matches on the other hand is a lot easier and faster to set on fire.

Cargo holds are pressurized on most commercial aircraft excepting quite small planes; certainly anything in the Singapore Airlines fleet would have a pressurized hold.